Most coatings used for finishing automobile and truck exteriors contain one or more film-forming polymers, optional crosslinking agents, and volatile organic solvents. The presence of volatile organic solvents is of concern, however, because they form the bulk of the emissions produced during application and curing of the coating composition which need to be controlled due to governmental regulations. Accordingly, there have been many attempts to reduce the emissions or VOC (volatile organic content) of such coatings.
One avenue for reducing regulated emissions has been to use waterborne coatings. While waterborne coating compositions offer lower emissions, they still contain significant amounts of organic co-solvent, and also have more elaborate and expensive handling and application requirements.
Powder coatings also have very low organic emissions but require complete reinvestment in the paint facilities and to date have not exhibited the appearance and other properties desired.
Another avenue for reducing regulated emissions has been to increase the solids content of solvent borne liquid coatings. The solids content of solvent borne liquid coatings can be increased by several methods, such as the use of lower molecular weight polymers or oligomers, and by using less organic solvent. The advantages of this approach include the exceptional appearance, durability and properties of such systems and the ability for them to be used in a current automotive plant with little or no change in facilities. At some point, however, the polymer solution becomes too viscous. This causes major problems with handling during manufacturing and also with the ability to spray or otherwise apply the coating onto the motor vehicle, thus requiring added solvent that increases the undesirable VOC content.
Another way to attain higher solids is to use reactive diluents, such as ethylene glycol or glycerol, in the final paint to keep the spray viscosity within acceptable limits. In these coatings, however, the film-forming polymer must be stripped of environmentally adverse hydrocarbon solvents that are used in the polymer synthesis before being introduced in the coating. The stripping step adds complexity, time and expense to the polymer synthesis and is therefore undesirable.
The object of the present invention is to provide an alternative to conventional environmentally hazardous organic liquid carrier solutions to attain high solids (low VOC) paints that can be applied with relative ease.